I'd like to shift gears now and talk about a personal concern.
Etymology: based on the idea that a vehicle will change speed when you change gears (= machine parts)
shift gears
To quickly or abruptly change what one is doing or discussing. With that out of the way, let's shift gears and discuss our strategy for the third quarter.About halfway into the story, the book shifts gears and begins a narrative from the perspective of the antagonist.